Coal treatment



Patented Got. 17, 1939 UNITED STATES 2,176,129 coAL TREATMENT Harvey13.. Fife, Pittsburgh, Pa.

No Drawing. Application October '26, 1937. Serial No. 171,098

6 Claims.

In the course of experience it has become a recognized fact thatcarbonaceous fuels of the various types designated broadly by the termcoal, are greatly improved by protective treat- 6 ment conducted at somestage between the mining and combustion of the coal. There are variousaspects to the protective treatment of coal, sounding in economy, insafetyjin cleanliness, and in uniformity of combustion qualities. From10 its nature coal is subject to degradation both by weathering and bymechanical breakage, the latter being the factor preponderantlyresponsible for the degradation 'of coal. Such breakage, when it occursat the mine, gives increased difficulty in sizing, and detracts fromthe'value of the coal, which, itmay be assumed, is most valuable when itis in a condition of approximately fly dust. In the tipple the coal isgraded as to size, as by screening, and a certain proportion of theslate forming the major inorganic contamination is removed. Theoperation of screening itself causes degradation, since the coalparticles as received in the tipple in some proportion fracture in thescreens to form smaller sizes, and by fracture and abrasion produce anincreased proportion of fines and of ily'dust. After coal has 40 beenscreened, it is not only in most instances exposed to weathering, but isinevitably exposed to the degradation-producing efiects oftranspontation and handling. For example, if domestic coal be loaded infreight cars and conveyed t'b 'a central depot, it is subject tobreakage while'b'elng loaded upon and unloaded from the cars, ahH -t'orubbing and jarring. during transit. A 'si possibility of degradationoccurs in a tru' veyance from a central depot to the po ultimate use,and in most instances the ther possibility of degradation in the r thecoal to the furnace, or into a stolf i'? be understood that throughouttheefi intervening between its mining and it dimensions and less, and acertain proportion of PATENT OFFICE tion the coal is subject to degi; ation of its exposed surface. 3 It may be assumed that all and to renderuseful and de Y which would otherwise be aste) possess undesirable feat'lary objects in the tre coal, and to sqm coal. Variou ,gra oil have beecoal by the application of a wax blend, such as petrolatum, cannot beconsidered to be practical merely in the fact that these materials areapplied indiscriminatelyto coal of various types at some stage in thehistory of the coal.

The conditions under which satisfactory treatment of coal may be mostreadily had are those in which a coal of good grade, clean andapproximately dust-free, is sized before treatment, and in thisconnection I mean by coal of good grade, a coal which is dense,relatively non-friable, and which does not possess marked cleavageplanes creating a tendency readily to fracture. Upon coal of that sortand under those conditions a treatment with petroleum oil even if ofrelatively low viscosity is advantageous, and the higher viscosity cutsof petroleum applied with heat in the form of a spray are in approximateproportion to increasing viscosity increasingly advantageous. It is alsopossible with reasonable satisfaction to apply petrolatum to clean,sized and relatively dust-free coal, by spraying, under simple airpressure, petrolatum rendered sprayable by being heated to above itsmelting point. When coal is clean and sized, petrolatum may also beapplied very satisfactorily by dipping the coal in a warm watersuspension of the petrolatum, or by a low pressure spraying of suchwater suspension upon the coal.

Coke may be considered as a clean and sized coal, and as such maysatisfactorily be treated by spraying it with petroleum oil or a wax-oilblend. As it may, however, be treated with advantage by the specializedmethod herein disclosed, I intend in the appended claims to include itby the generic term coal.

It may be generally stated that in comparison with a petroleum oil assuch, irrespective of the viscosity of the oil, a petrolatum in whichthere is any substantial content of wax is superior to a simple oil.Petrolatum does not crawl upon the surface of the coal, as does oil, andis less subject than oil to mechanical removal; thereby continuing formore extended periods of time and under more severe conditions ofhandling so to lubricate the coal as to minimize breakage, and also themore efficiently and for a longer period to minimize dust formation in abody of coal. Petrolatum by possessing a lesser tendency to crawl thandoes oil posssesses a further advantage over oil, in that it does not inlike manner collect in the receptacles or bins in which the coal istransported or stored.

Whether a simple oil or a plasticized wax, such as petrolatum, be usedfor the treatment of coal, departure from the ideal conditions abovedescribed increases the difliculty of satisfactory treatment. Thus intreating run-of-the-mine coal it is necessary in sprayingthe coal with atreating material that the spray be so finely atomized as to penetratethe mass of coal and to find lodgment upon all surfaces of each coalparticle. In order to obtain optimum results it is necessary that dustand fines present in the bodyof coal, and which when present in anyproportion by weight constitute a very large proportion of the surfacearea of the coal, should not take to themselves an undue proportion of acoating material during the treating operation. This is important fromthe viewpoint of economy, in order that the conduct of the process maybe efficient, and in order that the fines, such as coal particles frominch down, may not carry such quantity of the oil or wax that difficultyis experienced in pulverizing them for use in blowers and the like.

It should be further understood that in dealing with a mist of eitheroil or Wax so finely atomized as to be applied uniformly to the surfacesof the coal particles of various sizes, there is a fire and explosionhazard which must in practice be. given careful consideration. It mayalso be assumed that in order to cover the coal particles there must beeither an instantaneous flow of the material on the surface of the coalparticles, or the mist of oil or petrolatum (and this is particularlytrue in the case of petrolatum) must be so fine that the coal particlesare instantly covered by impingement with the mist. It may be noted thatin treating coal which has a substantial content of fly dust there is anelectrical phenomenon which must be taken into consideration from theviewpoint of safety. Coal dust particles readily take a staticelectrical charge and as charged are, when present in quantity,frequently capable of delivering a spark causing a dust explosion inwhich the mist of oil or wax, as well as the dust particles themselvesis involved. If high vis cosity oil or petrolatum are applied by airpressure spraying with the application of heat suffi cient to renderthem adequately sprayable, the mist thus produced has itself a staticcharge and is incapable of individually discharging the coal dustparticles within the spray zone. The same condition is encountered inthe simple air spraying of low viscosity oil. Coal dust being present invariable quantity, it is difficult to form an atomized mist of petroleumoil or petrolatum rich enough for satisfactory treatment withoutincurring serious explosion risks.

I have discovered that the association of steam in the spraying zonewith a finely atomized mist of petroleum oil, or the petroleum-derivedpetrolatum which has been above defined, greatly reduces explosion andfire hazards. I have further discovered that if such steam pass throughthe spraying zone at low velocity, and at a corresponding temperature,it is a useful adjunct in the actual deposition of the oilypetroleum-derived treating material upon the coal, and does not, likehigh velocity steam used for atomizing, detract from the effects desiredfrom deposition of the treating material on the coal. That is, it doesnot serve to carry coal dust and the atomized treating mist out ofcontact with the coal. In reducing explosion and fire hazards a steamdilution of the mist is more effective than an air dilution, bothbecause it does not itself provide an explosive mixture with either thehydrocarbon mist or the coal dust, and also because it servesindividually to discharge the static electrical charge carried by theparticles of the coal dust.

In accordance with my preferred procedure in treating run-of-the-minecoal at the tipple I pass the coal with agitation, as in a fallingstream, through a spraying zone in which it is acted upon by a mist offinely atomized petroleum treating material commingled with low velocitysteam. Atomization is in the case of high viscosity petroleum oil andpetrolatum effected by a pump pressure which is desirably high, forexample, a pump pressure of the order of 400 pounds per square inch andupward at the spraying nozzle, the spraying of the high viscosity oil orpetrolatum being facilitated by superatmospheric temperature, which inthe case of petrolatum is above the pour-point of petrolatum. In thecase of high viscosity oil, assuming that high pressure is used, atemperature which reduces the viscosity of the oil to from 600 Sayboltseconds at F. to 800 Saybolt seconds at 100 F. is adequate.

Desirably I utilize a steam coil to raise the temperature of thepetroleum treating material in passage to the spraying nozzle.

In spraying low viscosity oil in this manner, in association with lowvelocity steam, the oil need not under all conditions be preheated forspraying and application to the coal. For example, I have found itunnecessary to preheat oil of viscosity up to about 600 to 800 Sayboltseconds at 100 F. if the atomizing pressure be of the order of about 300pounds per square inch or rnore. For lower viscosity oils the pressuremay be proportionally decreased without recourse to preheating, and ifhigh viscosity oils are preheated to viscosities below 600 to 800Saybolt seconds at 100 F., the spraying pressure may be correspondinglylower than 400 pounds per square inch. At that pressure lean petrolatumblends having pour-points at unelevated temperature may be sprayedwithout preheating.

Whether the spraying be efiected by preheating or high pressure, orboth, the effect of the low velocity steam in the finely atomized mistis identical Since the steam which is added to the petroleum mist is notdepended upon to atomize the oil or petrolatum, it may be released atlow velocity, and I have with satisfaction utilized steam within aboiler pressure range of from 10 pounds per square inch to 250 poundsper square inch. If the steam is expanded at'the spraying nozzle, as forexample to surround the atomized mist of hydrocarbon material in a coneit is desirably an initially low pressure steam. If,.- however, thesteam to be expanded into the spraying zone at some point substantiallyremoved from the spraying nozzle a smaller quantity of steam at higherpressure is, when expanded, substantially equivalent in diluting themist with low velocity steam. 1

More specifically to describe my preferred .procedure, I have found itdesirable to provide one pound of steam for each pound of thehydrocarbon material. This ratio, however, is subject tovariation withinrelatively wide limits in accordance with the volume of the sprayingzone and other factors which may influence the effect of the steam. Thespraying zone is .established by the relative position of the sprayingnozzle, or nozzles, and the instrumentality which delivers the coal, andis also defined by instrumentalities which in practical effect confinethe treating mist to a limited volume. For example, I have found itdesirable to utilize a spray hood surrounding the spraying nozzle, ornozzles, and the end, or a limited region, of the apparatus whichconveys the coal.

When the coal is passed through the spraying zone in a falling stream,as is most desirable, I prefer to position the spraying nozzles as closeto the stream as is possible, and have found that I I may under mostcircumstances, and in treating run-of-the-mine coal position nozzleswithin a foot of the under side of the coal stream and may positionnozzles within three feet of the upper side of the coal stream. Thespraying zone isthus permitting them to coagulate. By giving up its heatof condensation in the spraying zone, the steam also contributes to theuniform thin distribution of the hydrocarbon material over the surfacesof the coal particles.

and thereby to remove from the tipple any such proportion .of thespraying mist and coaldust as may tend to escape from the spraying zone.

In considering the advantages of the treating process above described,it should be appreciated that run-of-the-mine coal frequently has aproportion of its surface equal to about to of the whole represented bycoal particles which are less than inch in dimension. Such fractionwould represent 10% to 30% the total weight of the coal. portion of thefines be formed into larger particles without gathering a largerproportion of the treating material than is commensurate with itssurface area. The portion below '200 mesh in particle size becomesparticles of non-flying character without so agglomerating the particlesthat immediate normal screening is inhibited. Also by preventing undueaccumulation of treating material by them, the more substantial finesare in better condition for subsequent pulverization, or immediatescreening. An additional advantage of the method is that the conditionof the mist leads to the coating of the slate content of therun-of-the-mine coal, thus protecting it against breakage in screeningand subsequent degradation into a particle size so small that it wouldtend to segregate in the lower region of a stored mass of the coal.

I have found that in preparation for screening and mechanical cleaning,if that be employed, a very thin deposit of petrolatum is sumcient tominimize degradation of the coal by fracture or abrasion during theseoperations. For example, I have obtained excellent results in preventingdegradation at the tipple by applying to run-ofthe-mine coal from 2.3pounds per ton to 2.5 pounds per ton of petrolatum, consisting of 70% byWeight wax and 30% by weight associated oil, in accordance with mypreferred procedure as outlined above. The surface area of a ton ofrun-of-the-mine coal is a variable quantity, because of varying breakageof the coal in mining. It is well therefore to explain that I haveobtained satisfactory results by applying petrolatum (70% wax content)to coal in a quantity of from .001'to .004 pound to each approximatesquare yard of coal surface. The quantity actually used within thisquantity range is roughly proportioned inversely to the ability of thecoal to withstand blows and abrasion.

While I have found wax-free petroleum oil to be less effective inprotecting run-of-the-mine coal against degradation at the tipple thanis petrolatum, advantage in minimizing fire and explosion hazards, andin degree in lessening waste of treating material, is obtained by atreatment similarly conducted with oil.

When conducting my process with petroleum oil, instead of petrolatum, asthe oily petroleum treating material, like quantities by weight of oilper .unit area of coal surface are desirably applied. This is so,although the oil is less efiective' than an equal quantity of petrolatumin protect- It is important that the fly dust ing the coal againstbreakage and abrasion, for the reason that the application of an unduequantity of oil to the coal seriously interferes with the normaloperation of screening.

For certain uses, it is desirable to apply an added coating (preferablypetrolatum) to the coal after screenings Such final treatment is ofparticular utility in the case of stoker coal and other domestic sizes,which have had their dust content removed by screening. Although in suchtreatment the dust problem is negligible, the reduction in fire andexplosion hazard renders the addition of low velocity steam to anotherwise atomized treating mist of great practical importance. Sincethis final treatment may be conducted outside the tippleor otherenclosure, the use of the low velocity steam may be associated with anair or steam atomization of the oily petroleum treating material tocounteract the fire and explosion hazards of such spraying, and todecrease the waste of finely atomized mist attendant upon air or steamspraying.

It may be assumed that in the pretreatment of coal in the tipple,petroleum oil may with fair satisfaction be used upon coal of the sortswhich are of themselves particularly resistant to breakage and abrasion.In a final treatment of coal petrolatum has universal advantage overpetroleum oil, due to the increased life of a petrolatum film ascompared with an oil film on coal, and in the superior cleanliness ofcoal treated with petrolatum. I do not, however, exclude from a finaltreatment conducted in accordance with my method, petroleum oil as theoily petroleum treating material used.

In this final, or secondary, treatment I have found it desirable toincrease the quantity oi. applied coating material to from .006 to .(lli pound per square yard of coal surface, and if the noncrawlingpetrolatum be employed, I have found it desirable so to place the spraynozzles that a greater proportional quantity of the film is deposited onthe larger coal particles. .This permits collection of dust particles oncoal particles of those sizes from which dust particles are least likelyto be-removed by wiping. Since such relatively thick film is of anon-crawling nature it may continue to function in dust collectionduring long continued storage and handling. The above selectiveapplication of petrolatum I efl'ect by so distributing the number ofspray nozzles that a preponderant proportion of the treating materialreaches the upper side of a coal stream as it changes its direction tofall by gravity from a boom, or the like apparatus.

It'is to be understood that when-I speak of petroleum oil I mean eitherparaffln base, mixed base, or asphalt base petroleum oil; and althoughasphalt base petroleum does not serve as a source of petrolatum, it maybe used in blending with wax artificially to produce a wax-oil blendresponding to my definition of petrolatum.

I claim as my invention:

1. The herein described method of protectively treating coal withoilypetroleum material which comprises atomizing an oily petroleummaterial into a fine mist by subjecting it to extraneous mechanicalpressure at a spray nozzle, and while passing the coal to be treatedthrough a treating zone of the said finely atomized mist independentlyadding steam at low velocity and lowtemperature to the said finelyatomized mist, to supply to the coal independently of the said mist heatfor flowing the oily petroleum material of the mist over the coal and toapply moisture at the surface of the coal.

2. The herein described method of protectively treating coal withpetrolatum which comprises atomizing petrolatum intoa fine mist bysubjecting it to extraneous mechanical pressure at a spray nozzle, andwhile passing the coal to be treated through a treating zone of the saidfinely atomized mist independently adding steam at low velocity and lowtemperature to the said finely atomized mist to supply to the coalindependently of the said mist heat for flowing the petrolatum of themist over the coal and to apply moisture at the surface of the coal.

3. The herein described method of protectively treating coal with oilypetroleum material which comprises forming and projecting a finelyatomized mist of an oily petroleum material at a spray nozzle bysubjecting it to extraneous mechanical pressure, and while passing thecoal to be treated through the said mist of oily petroleum materialconfining and diluting the said finely atomized mist by independentlyand simultaneously projecting toward the coal a mist of low velocity lowtemperature steam serving also to supply to the coal heat for flowingthe oily petroleum material over the coal and serving to apply moistureat the surface of the coal.

4. The herein described method of protectively treating coal withpetrolatum which comprises forming and projecting a finely atomized mistof petrolatum at a spray nozzle by subjecting it to extraneousmechanical pressure, and while passing the coal to be treated throughthe said mist of petrolatum confining and diluting the said finelyatomized mist by independently and simultaneously projecting toward thecoal a mist of low velocity low temperature steam serving also to supplyto the coal heat for flowing the petrolatum over the coal and serving toapply moisture at the surface of the coal.

5. The herein described method of protectively treating screened coalwith oily petroleum material which comprises atomizing oily petroleummaterial into a fine mist in a spray nozzle, and

,directing the said finely atomized mist of oily petroleum treatingmaterial upon coal which has previously been screened whileindependently and simultaneously projecting upon the said screened coallow velocity low temperature steam to supply to the coal independentlyof the said mist of oily petroleum material heat for flowing the oilypetroleum material over the coal and to apply moisture at the surface ofthe coal.

6. The herein described method of protectively treating screened coalwith petrolatum which comprises atomizing petrolatum into a fine mist ina spray nozzle, and directing, the said finely atomized mist ofpetrolatum upon coal which has previously been screened whileindependently and simultaneously projecting upon the said screened coallow velocity low temperature steam to supply to the coal independentlyof the said petrolatum mist heat for flowing the petrolatum over thecoal and to apply moisture at the surface of the coal.

HARVEY R. FIFE.

